Polyamide multifilament and knitted lace manufactured using same

ABSTRACT

A polyamide multifilament has a single-filament fineness of 0.8 dtex to 7 dtex, a strength of 7.5 cN/dtex to 8.5 cN/dtex, and a knot strength of 6.0 cN/dtex to 7.5 cN/dtex. The polyamide multifilament may have a tensile strength at 15% elongation of 6.1 cN/dtex to 7.5 cN/dtex. The polyamide multifilament may have a total fineness of 20 dtex to 44 dtex.

TECHNICAL FIELD

This disclosure relates to a polyamide multifilament suitable for a knitted lace, more particularly, to a polyamide multifilament being, when the polyamide multifilament is used as a ground lace yarn, capable of providing a knitted lace having excellent durability, a beautiful pattern, and a good texture.

BACKGROUND

Polyamide fibers and polyester fibers, which are synthetic fibers, are in extensive use in clothing and industrial applications because of their excellent properties regarding mechanical and chemical properties. In particular, polyamide fibers are excellent in terms of the peculiar softness, high strength, colorability in dyeing, heat resistance, hygroscopicity and the like, and are, hence, in extensive use in general clothing applications including stockings, innerwear, and sportswear.

As consumer needs for lace, a lace with a beautiful pattern and a soft texture is desired. To make the lace pattern look beautiful, it is necessary to make yarns constituting a ground structure to have an enhanced fineness. However, along with the enhancement of the fineness, the strength of the yarns decreases so that higher strength is desired. In addition, along with the enhancement of the fineness of the yarns constituting the ground structure, a yarn ratio of a pattern yarn increases and, thus, a stress applied to an intersection part of ground yarns is stronger. Accordingly, it is also desired to increase the durability of the intersection part. Further, to soften the texture of the lace, it is strongly desired to enhance the fineness of the single yarn constituting the ground structure.

To increase the strength of the polyamide fibers to be high, for example, JP-A-2008-31572 proposes a nylon-6 fiber for fishing nets having a fineness of 250 dtex to 4400 dtex, which provides net cloth having excellent durability and weather resistance, high strength and high toughness, and a fishing net using the same.

JP-A-2004-11082 discloses a polyamide fiber having a fineness of 300 dtex to 1,000 dtex, which has excellent shock absorption against shear stress and multi-directional impact, and excellent durability and fatigue resistance when the polyamide fiber is subjected to a knitting process and used for industrial materials, and a knit using the fiber.

However, since the fibers described in JP '572 and JP '082 have a large fineness, the lace transparency cannot be obtained, and the fibers are not suitable for a knitted lace. In addition, since the single yarn has a large single-filament fineness, the texture of the knitted lace is not satisfactory.

It could therefore be helpful to provide a high-strength polyamide multifilament having excellent durability even in the enhancement of the fineness and the single-filament fineness. More particularly, it could be helpful to provide, by using a polyamide multifilament having high strength and high knot strength, a knitted lace having excellent processability through high-order processing and product appearance quality, maintains the same level of strength as products in the related art, can achieve the enhancement of the fineness and the single-filament fineness, maintains the durability of the lace, has a beautiful pattern due to transparency of the ground lace yarn, and has an excellent texture.

SUMMARY

We thus provide:

-   (1) A polyamide multifilament having a single-filament fineness of     0.8 dtex to 7 dtex, a strength of 7.5 cN/dtex to 8.5 cN/dtex, and a     knot strength of 6.0 cN/dtex to 7.5 cN/dtex. -   (2) The polyamide multifilament according to (1), having a tensile     strength at 15% elongation of 6.1 cN/dtex to 7.5 cN/dtex. -   (3) The polyamide multifilament according to (1) or (2), having a     total fineness of 20 dtex to 44 dtex. -   (4) A knitted lace produced using the polyamide multifilament     according to any one of (1) to (3) as a ground lace yarn. -   (5) A method of producing the polyamide multifilament according to     any one of claims (1) to (3), the method including:

ejecting a molten polyamide resin from a spinneret to form filaments;

cooling and solidifying each of the filaments; and

drawing the obtained filaments,

in which the method is performed using a polyamide multifilament production device including at least:

a spinneret for ejecting a molten polyamide resin to form filaments;

a heating cylinder for gradually cooling the filaments;

a cooling device for cooling and solidifying the filaments;

a fluid swirling nozzle device for imparting convergence to yarns by a swirling flow;

a take-up roller for taking-up and drawing the filaments; and

a drawing device for drawing the filaments, and

in which the following conditions (A) to (D) are satisfied:

(A) the heating cylinder is provided above the cooling device;

(B) the fluid swirling nozzle device is provided above the take-up roller;

(C) the drawing device is a multi-stage drawing device having two or more stages; and

(D) a low relaxation heat treatment is performed immediately after multi-stage drawing.

(6) The method of producing the polyamide multifilament according to (5), in which the relaxation heat treatment is performed between a drawing roller and a relaxing roller at a relaxing ratio of 0 to 1.5% and a heat set temperature of 150° C. to 200° C.

The polyamide multifilament is a polyamide multifilament having high strength and high knot strength. Further, using the polyamide multifilament, it is possible to obtain a knitted lace having processability through high-order processing and product appearance quality, maintains the durability of the lace, has a beautiful pattern due to transparency of the ground lace yarn, and has an excellent texture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a production device which can be preferably used for producing a polyamide multifilament.

FIG. 2 shows one example of a production device illustrated as a comparison of the production of the polyamide multifilament.

FIG. 3 is a schematic cross-sectional model diagram showing a spinneret and a heating cylinder which can be preferably used in the production of the polyamide multifilament according to the example.

FIG. 4 shows an example of a swirling nozzle which can be preferably used for producing the polyamide multifilament.

REFERENCE SIGNS LIST

-   1: spinneret -   2: gas feeder -   3: heating cylinder -   4: cooling device -   5: oiling device -   6: fluid swirling nozzle device -   7: take-up roller -   8: first drawing roller -   9: second drawing roller -   10: relaxing roller -   11: entanglement imparting device -   12: winding device -   L: length of multilayered heating cylinder -   L1: single-layer length of multilayered heating cylinder -   LS: cooling initiation distance -   Lg: oiling position -   LA: length of swirling nozzle

DETAILED DESCRIPTION

Hereinafter, our multifilaments and knitted lace will be described in more detail.

The polyamide multifilament includes a polyamide. Such a polyamide is a resin including a high molecular weight substance in which a so-called hydrocarbon group is linked to the main chain via an amide bond.

Such a polyamide is excellent in spinnability and mechanical properties, and is preferably one mainly containing polycaproamide (nylon-6) or polyhexamethyleneadipamide (nylon-66). One mainly containing polycaproamide (nylon-6) is more preferred because of the unsusceptibility to gelation and satisfactory spinnability thereof.

The above polycaproamide contains ε-caprolactam as a constitutional unit, and 80 mol % or more thereof is constituted by ε-caprolactam. The above polycaproamide preferably contains 90 mol % or more of ε-caprolactam. The above polyhexamethyleneadipamide contains hexamethylene diammonium adipate as a constitutional unit, and 80 mol % or more thereof is constituted by hexamethylene diammonium adipate. The above polyhexamethyleneadipamide preferably contains 90 mol % or more of hexamethylene diammonium adipate.

Other components are not particularly limited, and examples thereof include units of aminocarboxylic acids, dicarboxylic acids, diamines, and the like which are monomers for constituting polydodecanoamide, polyhexamethyleneadipamide, polyhexamethyleneazelamide, polyhexamethylenesebacamide, polyhexamethylenedodecanoamide, poly-m-xyleneadipamide, polyhexamethyleneterephthalamide, polyhexamethyleneisophthalamide and the like.

To effectively produce the desired effects, it is preferable that the polyamide contains none of various additives including delustering agents such as titanium oxide. However, the polyamide may contain various additives, e.g., a heat resistance improver, as long as the inclusion thereof does not impair the desired effects. The additives may be mixed as necessary in a content of 0.001 wt% to 0.1 wt% with respect to the polymer.

The polyamide multifilament is characterized in that the single-filament fineness, the strength, and the knot strength thereof are all within the specific ranges described above.

Typically, by enhancing the fineness of the polyamide multifilament, a knitted lace having increased transparency of the ground lace yarn and a beautiful pattern can be obtained, but the product strength is reduced and the durability of the lace is reduced. In addition, since the yarn ratio of the pattern yarn increases, the stress applied to the ground yarn at the intersection part is increased. Therefore, to maintain the durability, it is necessary to increase the strength and the knot strength. Further, to soften the texture of the lace, it is necessary to enhance the single-filament fineness.

Therefore, we discovered that to provide a knitted lace having excellent texture and durability, increased transparency of the ground lace yarn, and a beautiful pattern, it is important to set the single-filament fineness, the strength, and the knot strength within the above specified ranges.

The polyamide multifilament has a single-filament fineness of 0.8 dtex to 7 dtex. Within such a range, a lace having a soft texture is obtained. When the single-filament fineness is larger than 7 dtex, the texture of the lace becomes stiff. When the single-filament fineness is less than 0.8 dtex, due to a high tension state, fretting on a guide and the like, in a spinning step and a high-order processing step, the strength is lowered and fluffing is likely to occur, and filament breakage in the high-order processing step increases and the product strength and appearance quality are lowered. The single-filament fineness is preferably 3.0 dtex to 6.6 dtex.

The polyamide multifilament has a strength of 7.5 cN/dtex to 8.5 cN/dtex. Within such a range, the durability of the lace is improved, and the fineness for achieving transparency can be enhanced. When the strength is less than 7.5 cN/dtex, the durability of the lace is lowered. When the strength is larger than 8.5 cN/dtex, due to the high tension state, the fretting on the guide and the like, in the spinning step and the high-order processing step, fluffing is likely to occur, and filament breakage in the high-order processing step increases and the product appearance quality is lowered. The strength is preferably 7.7 cN/dtex to 8.2 cN/dtex.

Since the knitted lace has a special knitting structure, the force concentrates at the intersection point of the ground yarn and the pattern yarn. Therefore, increasing not only the strength in a fiber axis direction but also the knot strength is important for the durability of the lace. That is, in addition to improving the strength in the fiber axis direction, improving the strength of a stress concentration portion at the intersection point improves the durability of the lace.

Improving the knot strength is particularly effective for the polyamide multifilament having a high fineness. When the fineness of the ground yarn is enhanced to achieve the transparency of the ground lace yarn, the yarn ratio of the pattern yarn increases and, as a result, the stress applied to the intersection part of the ground yarn increases. Therefore, when the knot strength is improved, the fineness can be enhanced.

The polyamide multifilament has a knot strength of 6.0 cN/dtex to 7.5 cN/dtex. Within such a range, the durability of the lace is improved, and the fineness for achieving transparency can be enhanced. When the knot strength is less than 6.0 cN/dtex, the filament cannot withstand the stress applied to the intersection point of the ground yarn and the pattern yarn and breaks, and the durability of the lace is lowered. The larger the knot strength, the more preferable. However, an upper limit thereof is 7.5 cN/dtex. The knot strength is preferably 6.3 cN/dtex to 7.5 cN/dtex.

The polyamide multifilament preferably has a tensile strength at 15% elongation (hereinafter, may be referred to as “15% strength”), which is an index of raw yarn properties, of 6.1 cN/dtex to 7.5 cN/dtex. The 15% strength is determined by making a measurement in accordance with JIS L1013(2010), Tensile Strength and Elongation, drawing a tensile strength-elongation curve, dividing the tensile strength (cN) at 15% elongation by the total fineness, and taking the resultant value as the 15% strength. The 15% strength is a value roughly representing the fiber modulus, and a high 15% strength indicates that the inclination of the tensile strength-elongation curve is large and the fiber modulus is high. On the other hand, a low 15% strength indicates that the inclination of the tensile strength-elongation curve is low and the fiber modulus is low.

As will be described later, the polyamide multifilament is subjected to a multi-stage and high-ratio drawing. A high fiber modulus is achieved by the high-ratio drawing, and particularly, the occurrence of fluffing is prevented while a high fiber modulus is achieved by multi-stage drawing.

Since the polyamide multifilament has a 15% strength of 6.1 cN/dtex to 7.5 cN/dtex, the product appearance quality is improved. When the 15% strength is 6.1 cN/dtex or more, changes in the fiber structure and the crystal orientation in a dyeing step are small, the shrinkage of the fiber is prevented, and the rigidity of the fiber is easily maintained. That is, the dimensional change and shrinkage unevenness during heat setting in a lace production step are reduced, the surface of the fabric becomes smooth and beautiful, and the product appearance quality is improved. When the 15% strength is 7.5 cN/dtex or less, the filament breakage and the occurrence of fluffing in the high-order processing step are prevented, and the product appearance quality is improved. The 15% strength is preferably 6.4 cN/dtex to 6.9 cN/dtex.

The polyamide multifilament preferably has a strength-elongation product of 9.5 cN/dtex or more. When the strength-elongation product is 9.5 cN/dtex or more, the durability of the lace is good, the filament breakage in the high-order processing step is little, and the processability through high-order processing is good. The polyamide multifilament more preferably has a strength-elongation product of 10.0 cN/dtex or more. The larger the strength-elongation product, the more preferable. However, an upper limit thereof is about 11.5 cN/dtex.

The polyamide multifilament preferably has a total fineness of 20 dtex to 44 dtex. Within such a range, a knitted lace having a beautiful pattern, an excellent texture, and good durability is obtained. When the total fineness is 44 dtex or less, a knitted lace having increased transparency of the ground lace yarn, a beautiful pattern, and a soft texture is obtained. When the total fineness is 20 dtex or more, the strength and the knot strength are sufficient, and the durability of the lace is good. The total fineness is more preferably 22 dtex to 33 dtex.

The polyamide multifilament preferably has a fineness variation value U %, which is an index of thickness unevenness in the longitudinal direction of the fiber, of 1.2% or less. Within such a range, after the knitted lace is dyed, there are no stains or streaks due to the unevenness of the multifilament, and the product appearance quality is good. The fineness variation value U % is more preferably 1.0% or less. The smaller the U %, the more preferable. However, a lower limit thereof is about 0.4%.

The cross-sectional shape of the polyamide multifilament is not particularly limited. For example, the multifilament may have a circular cross-section, a flat cross-section, a lens-shaped cross-section, a trifoliate cross-section, a multilobar cross-section, an irregular cross-section having three to eight protrusions and the same number of recesses, a hollow cross-section, or any other common irregular cross-sections.

We also provide a method of producing the above polyamide multifilament. The method of producing the polyamide multifilament includes steps of ejecting a molten polyamide resin from a spinneret to form filaments, cooling and solidifying each of the filaments, and drawing the obtained filaments.

This method is performed using a polyamide multifilament production device including at least (1) a spinneret for ejecting a molten polyamide resin to form filaments, (2) a heating cylinder for gradually cooling the filaments, (3) a cooling device for cooling and solidifying the filaments, (4) a fluid swirling nozzle device for imparting convergence to yarns by a swirling flow, (5) a take-up roller for taking-up and drawing the filaments, and (6) a drawing device for drawing the filaments.

In this method, the following conditions (A) to (D) are satisfied:

(A) the heating cylinder is provided above the cooling device;

(B) the fluid swirling nozzle device is provided above the take-up roller;

(C) the drawing device is a multi-stage drawing device having two or more stages; and

(D) a low relaxation heat treatment is performed immediately after multi-stage drawing.

Hereinafter, an example of the method of producing the polyamide multifilament will be described in detail. FIG. 1 shows one example of a production device which can be preferably used to produce the polyamide multifilament according to the example.

The polyamide multifilament may be produced in the following manner. A poly-amide resin is melted, and the polyamide polymer is weighed and transported by a gear pump and finally extruded through ejection holes formed in a spinneret 1, thereby forming filaments. The filaments ejected from the spinneret 1 are passed through the following parts shown in FIG. 1: a gas feeder 2, which ejects steam to prevent the spinneret from being fouled with the lapse of time; a heating cylinder 3 disposed for gradual cooling to entirely surround the ejected filaments; and a cooling device 4. The filaments are cooled to room temperature and solidified in the cooling device 4. Thereafter, an oil is applied to the filaments with an oiling device 5 and the filaments are collected to form a multifilament, which is entangled with a fluid swirling nozzle device 6, is subjected to a two-stage drawing in a take-up roller 7, a first drawing roller 8, and a second drawing roller 9, and is then relaxed in a relaxing roller 10. The relaxed yarns are entangled by an entanglement imparting device 11 and are wound by a winding device 12.

In the production of the polyamide multifilament, it is preferable that the polyamide resin has a sulfuric acid relative viscosity of 2.5 to 4.0. Within such a range, a polyamide multi-filament having high strength, knot strength and strength-elongation product can be obtained.

The melting temperature is preferably higher by 20° C. to 95° C. than the melting point (Tm) of the polyamide.

In the production of the polyamide multifilament, the heating cylinder 3 is provided above the cooling device 4 to entirely surround the filaments. By providing the heating cylinder 3 above the cooling device 4 and regulating the atmosphere temperature within the heating cylinder to be within 100° C. to 300° C., the polyamide polymer ejected from the spinneret 1 can be caused to undergo orientation relaxation without thermal deterioration. As a result of the orientation relaxation due to gradual cooling from the spinneret surface to the cooling, a multifilament having high strength, 15% strength, and strength-elongation product can be obtained. When the heating cylinder is omitted, the orientation relaxation due to gradual cooling from the spinneret surface to the cooling is insufficient and it tends to be difficult to obtain fibers of which all of the strength, the 15% strength and the strength-elongation product are satisfactory.

In the production of the polyamide multifilament, the heating cylinder preferably has a multilayer configuration. When the temperature distribution in the heating cylinder is constant in a high fineness or high single-filament fineness region for clothing such as the polyamide multifilament, the thermal convection is prone to be disordered to affect the solidification of the filaments and this is a factor of deterioration of the U %. A heating cylinder having a multilayer configuration is hence disposed and temperatures are set to decline in stages from upper layers to lower layers. Thus, thermal convection from upper layers to lower layers is intentionally generated to produce a descending air flow in the same direction as the flow accompanying the filaments. As a result, disorder of the thermal convection in the heating cylinder is prevented and filament oscillation is reduced, thereby obtaining a multifilament having a small U %.

The length L of the multilayered heating cylinder, although depending on the fineness of the filaments, is preferably 40 mm to 100 mm. It is preferable that the multilayered heating cylinder has two or more layers, and the single-layer length L1 of the multilayered heating cylinder is preferably within the range of 10 mm to 25 mm.

The atmosphere temperature in the multilayered heating cylinder is 100° C. to 300° C., and it is preferable to form a gentle temperature gradient between the layers. For example, when the length L of the multilayered heating cylinder is 75 mm and the single-layer length L1 is 25 mm, the heating cylinder has a three-layer configuration, the upper layer has an atmosphere temperature of 250° C. to 300° C., the middle layer has an atmosphere temperature of 200° C. to 250° C., and the lower layer has an atmosphere temperature of 100° C. to 200° C.

Due to this configuration, an atmosphere temperature profile from the spinneret to the cooling can be controlled in stages over 100° C. to 300° C., thereby obtaining a polyamide multifilament having high strength, satisfactory 15% strength, high strength-elongation product, and good U %.

In the production of the polyamide multifilament, use can be made of any of methods in which the cooling device 4 is a cooling device configured to eject cooling/rectifying air from a certain direction, or an annular cooling device configured to eject cooling/rectifying air from the peripheral side toward the center, or an annular cooling device configured to eject cooling/rectifying air from the center side toward the periphery or the like.

The vertical distance LS (hereinafter referred to as “cooling initiation distance LS”) from the lower surface of the spinneret to the upper end of the cooling-air ejection part of the cooling device 4 is preferably 159 mm to 219 mm from the standpoints of preventing filament oscillation and reducing U %, and is more preferably 169 mm to 189 mm. With respect to the speed of the cooling air ejected from the cooling-air ejection surface, it is preferable that the velocity thereof is within the range of 20.0 m/min to 40.0 m/min in terms of average for the zone from the upper end to the lower end of the cooling-air ejection part, from the standpoints of the strength, strength-elongation product, and U %.

In the production of the polyamide multifilament, the position of the oiling device 5, that is, the vertical distance Lg (hereinafter referred to as “oiling position Lg”) from the lower surface of the spinneret to the position of the oiling nozzle of the oiling device 5 in FIG. 1, is preferably 800 mm to 1,500 mm, and more preferably 1,000 mm to 1,300 mm, although the distance Lg depends on the single-filament fineness and the efficiency of cooling of the filaments by the cooling device.

When the distance Lg is 800 mm or more, the temperature of the filaments declines to a temperature suitable for the oiling. When the distance Lg is 1,500 mm or less, the filament oscillation due to the descending air flow is small and a multifilament having a small U % can be obtained. In addition, when the distance Lg is 1,500 mm or less is preferred from the standpoints of the strength, the strength-elongation product, and the 15% strength, since the distance from the solidification point to the oiling position is short, resulting in a diminished accompanying flow and a reduced spinning tension and hence the spinning orientation is reduced and the drawability is excellent. When the distance Lg is 800 mm or more, the bending of the filaments in the zone from the spinneret to the oiling guide is appropriate and the filaments are less apt to be affected by fretting on the guide, thereby preventing the strength-elongation product and the 15% strength from decreasing.

In the production of the polyamide multifilament, the fluid swirling nozzle device 6 is provided over the take-up roller 7. JP '572 has proposed to perform drawing while performing an entanglement treatment during the drawing. This is effective in the single-filament thick region for industrial use, but in a high fineness or high single-filament fineness region for clothing such as the polyamide multifilament, when the entanglement treatment is performed during the drawing, the entanglement of the single yarn is likely to occur. Further, since an entanglement point is formed, the drawability of the yarn at the entanglement point is lowered during the drawing under a high tension, and the stress concentrates on the other part where the entanglement is not applied. As a result, the strength is lowered and fluffing is likely to occur. Therefore, by applying a fluid swirling nozzle before the drawing and imparting appropriate convergence to the yarn without entanglement points, uniform drawing is performed and a polyamide multifilament having high strength and no fluff can be obtained.

The fluid swirling nozzle has a shape as shown in FIG. 4, and a swirling flow from one direction in the cylinder imparts the convergence to the yarn. The length LA of the swirling nozzle depends on the fineness of the filament, and is preferably 5 mm to 50 mm from the viewpoint of imparting the convergence.

The injection pressure of the swirling flow is preferably 0.05 MPa to 0.20 MPa. When the injection pressure is within such a range, appropriate convergence can be imparted to the filaments, drawability does not decrease during the drawing under a high tension, and a single yarn disengagement does not occur during the drawing. Therefore, a high-strength polyamide multifilament without fluffing can be obtained while the enhancement of the fineness and the single-filament fineness is ensured.

In the production of the polyamide multifilament, the drawing is multi-stage drawing having two or more stages. In one-stage drawing, when high-ratio drawing is applied to obtain a raw yarn having a high fiber modulus and high strength, the drawing tension is high and the draw point is located on the take-up roller. As a result, the drawability is deteriorated, the strength is lowered, and fluffing is likely to occur. With the multi-stage drawing having two or more stages, the load applied to the yarn during the drawing is dispersed, the draw point is stable between rollers, the drawability is stable, and a polyamide multifilament having high strength, high fiber modulus, appropriate 15% strength and no fluff can be obtained.

The total draw ratio is preferably 3.5 to 5.0 times, and more preferably 3.8 to 4.7 times, to obtain the strong elongation range specified herein. The draw ratio at the first stage is preferably 2.5 to 3.5 times, and more preferably 2.7 to 3.3 times. During the drawing, the take-up roller 7 is heated to 40° C. to 60° C., the first drawing roller 8 is heated to 130° C. to 170° C., and the second drawing roller 9 is heated to 150° C. to 200° C. (heat set temperature). The speed of the take-up roller 7 is preferably 500 m/min to 1,300 m/min, and more preferably 700 m/min to 1,100 m/min.

In the production of the polyamide multifilament, the relaxing ratio [(speed of drawing roller−speed of relaxing roller)/(speed of relaxing roller)×100] between the drawing roller 9 and the relaxing roller 10 is preferably 0 to 1.5%. Within such a range, the relaxing ratio is lower than in producing a typical polyamide multifilament, and the heat setting is in a state of less relaxation (low relaxation heat treatment), and thus the linearity of the molecular chain is improved, and an amorphous portion in the fiber is uniformly and moderately stretched. Therefore, a polyamide multifilament having high strength, high knot strength, and high strength-elongation product can be obtained. When the relaxing ratio is larger than 1.5%, the heat is set in a state of large relaxation, such that the linearity of the molecular chain is lowered, and the strength and the knot strength are lowered.

For example, when the conditions in the direct spinning drawing method as shown in FIG. 1 is adopted, a polyamide multifilament having a high single-filament fineness of 0.8 dtex to 7 dtex, a high strength of 7.5 cN/dtex to 8.5 cN/dtex, and a high knot strength of 6.0 cN/dtex to 7.5 cN/dtex can be obtained.

The polyamide multifilament is fed as a ground yarn being a raw yarn to a lace knitting machine to knit a lace fabric by an ordinary method. The lace fabric may be one of any of ordinary knit stitches such as an embroidery lace, a raschel lace, or a leaver lace.

With respect to conditions for dyeing after the knitting, following post-processing, and final setting, these steps may be conducted by common methods. It is not limited to use dyes include acid dyes and reactive dyes, and the dyeing is not limited in color and the like.

EXAMPLES

Hereinafter, our multifilaments and knitted lace will be described in more detail with reference to the Examples.

A. Strength, Elongation, Strength-Elongation Product, and 15% Strength

A fiber sample was examined in accordance with JIS L1013 (2010), Tensile Strength and Elongation, to draw a tensile strength-elongation curve. The test conditions included a constant-rate extension type tester, a chuck-to-chuck distance of 50 cm, and a stretching speed of 50 cm/min. When the tensile strength at break was lower than the maximum strength, the maximum tensile strength and the corresponding elongation were measured. The strength and the strength-elongation product were determined using the following equations:

Elongation=elongation at break(%)

Strength=[tensile strength at break(cN)]/[total fineness(dtex)]

Strength-elongation product={strength(cN/dtex)}×{elongation(%)+100}/100

15% strength=[tensile strength at 15% elongation(cN)]/[total fineness (dtex)].

B. Knot Strength

In accordance with JIS L1013 (2010), Knot Strength, a knot portion was formed in the center of the chunk of the sample, and the measurement was performed under the same conditions as the above strength and elongation measurement. The knot strength was determined using the following equation:

Knot strength=[tensile strength at break(cN)]/[total fineness (dtex)].

C. Total Fineness and Single-Filament Fineness

A fiber sample was set on a sizing reel having a circumference of 1.125 m, and the sizing reel was rotated to make 500 turns to produce a looped hank. The hank was dried in a hot-air drying oven (105±2° C.×60 min) and weighed with a balance. The measured weight was multiplied by a standard moisture regain, and the fineness was calculated from the resultant value. The standard moisture regain was assumed to be 4.5%.

D. Sulfuric Acid Relative Viscosity (ηr)

A polyamide chip sample in an amount of 0.25 g was dissolved in sulfuric acid having a concentration of 98 mass % so that the sample amount was 1 g per 100 mL of the sulfuric acid. Using an Ostwald viscometer, the solution was examined for a flow time (T1) at 25° C. Subsequently, the sulfuric acid alone having a concentration of 98 mass % was examined for a flow time (T2). The ratio of T1 to T2, i.e., T1/T2, was taken as the sulfuric acid relative viscosity.

E. U %

Using USTER TESTER IV, manufactured by Zellweger Uster AG, a fiber sample was examined under the conditions of: sample length, 500 m; test yarn speed V, 100 m/min; twister (rotation speed), type S at 30,000/min; and 1/2 Inert.

F. Fluff Number

The obtained fiber sample was rewound at a speed of 500 m/min, a laser fluff detector was installed at a position 2 mm away from the yarn being rewound, and the total number of detected defects was converted into the number per 100,000 m and shown.

G. Evaluation of Lace (a) Softness

A lace product was evaluated for relative softness by inspectors (five persons) rich in experiences in evaluating texture, using a nylon-6 multifilament having a fineness of 40 dtex and including 4 filaments and taking a knitted lace produced by the method same as in Example 1 as a reference.

The grades evaluated by the inspectors were averaged, and the average was rounded off to the nearest whole number. Grades 5, 4, 3, and 1-2 on average were indicated by S, A, B, and C, respectively:

-   -   5: highly excellent     -   4: slightly excellent     -   3: fair     -   2: slightly poor     -   1: poor.         S and A were regarded as acceptable in terms of softness.

(b) Durability

Bursting strength was evaluated in the following manner. Arbitrarily selected three portions were examined for bursting strength by the bursting strength test method according to JIS L1096 (2010), Mullen type method (method A), and an average value of the measured values was evaluated in the following four grades:

-   -   S: 150 kPa or more     -   A: 120 kPa or more but less than 150 kPa     -   B: 110 kPa or more but less than 120 kPa     -   C: less than 110 kPa.         S and A were regarded as acceptable in terms of durability.

(c) Product Appearance Quality (Fluff)

Number of pillings in a lace fabric: the number of pilling portions (a state where fibers on the surface of the knitted fabric were fluffed and the fluffs were further intertwined with each other to form small spherical lumps) per roll of the lace fabric was shown according to the following criteria:

-   -   S: 0 or more and less than 2     -   A: 2 or more and less than 5     -   B: 5 or more and less than 10     -   C: 10 or more.         S and A were regarded as acceptable in terms of appearance         quality.

(d) Process Passage Capability

Suitability for knitting: the number of yarn breakages which occurred during knitting per roll of lace fabric (80 m) was shown according to the following criteria:

-   -   S: 0 or more and less than 5 yarn breakages     -   A: 5 or more and less than 10 yarn breakages     -   B: 10 or more and less than 20 yarn breakages     -   C: 20 or more and less than 30 yarn breakages.         S and A were regarded as acceptable in terms of process passage         capability.

(e) Appearance Quality (Pattern Appearance)

A product was evaluated for relative degree of pattern appearance by inspectors (five persons). The grades evaluated by the inspectors were averaged, and the average was rounded off to the nearest whole number. Grades 5, 4, 3, and 1-2 on average were indicated by S, A, B, and C, respectively:

-   -   5: highly excellent     -   4: slightly excellent     -   3: fair     -   2: slightly poor     -   1: poor.         S and A were regarded as acceptable in terms of appearance         quality.

Example 1 Production of Polyamide Multifilament

Nylon-6 (N6) chips having a sulfuric acid relative viscosity (ηr) of 3.3 and a melting point of 225° C., as a polyamide, were dried in an ordinary method to result in a moisture content of 0.03 mass % or less. The nylon-6 chips thus obtained were melted at a spinning temperature (melting temperature) of 298° C. and ejected from a spinneret (ejection amount 38.6 g/min). The spinneret used had 20 holes, which were round and had a diameter of 0.25, and was for producing 4 yarns per spinneret.

The spinning was conducted using a spinning machine having the configuration shown in FIG. 1. The heating cylinder used was a two-layer heating cylinder having a heating cylinder length L of 50 mm and single-layer lengths L1 and L2 of 25 mm each. Temperatures were set so that the atmosphere temperature in the upper layer of the heating cylinder was 300° C. and the atmosphere temperature in the lower layer of the heating cylinder was 150° C. The filaments ejected from the spinneret were gradually cooled at atmosphere temperatures of 150° C. to 300° C. in the two-layer heating cylinder and passed through the cooling device 4 having a cooling initiation distance LS of 169 mm and supplying 18° C. cool air at a speed of 35 m/min. Thus, the filaments were cooled to room temperature and solidified. Thereafter, the filaments were collected, while being oiled at an oiling position Lg of 1,300 mm, in terms of distance from the spinneret surface, thereby forming a multifilament. The fluid swirling nozzle device 6 having a swirling nozzle length LA of 25 mm was used to impart convergence. The convergence was imparted by injecting high-pressure air to the running yarn in the fluid swirling nozzle device 6 in the direction of the arrow. The pressure of the air injected was 0.1 MPa (flow rate 15 L/min). Thereafter, the multifilament was subjected to a first stage drawing such that the draw ratio between the take-up roller 7 and the first drawing roller 8 was 2.9 times, and then subjected to a second drawing such that the draw ratio between the first drawing roller 8 and the second drawing roller 9 was 1.5 times. Subsequently, 1.0% of relaxation was applied between the second drawing roller 9 and the relaxing roller 10, the yarn was entangled by the entanglement imparting device 11, and then wound by the winding device 12. At this time, the total draw ratio represented by a ratio of the take-up speed to the draw speed was adjusted to 4.35 times. The surface temperature of each roller was set such that the take-up roller was 40° C., the first drawing roller was 150° C., and the second drawing roller was 185° C., and the relaxing roller was equal to room temperature. The entanglement treatment was performed by injecting high-pressure air from the direction perpendicular to the running yarn in the entanglement imparting device. The pressure of the air injected was 0.2 MPa. Thus, a nylon-6 multifilament having a fineness of 33 dtex and including 5 filaments was obtained.

The nylon-6 multifilament obtained was evaluated, and the results thereof are shown in Table 1.

Production of Knitted Lace

Next, the multifilament was warped and set as a back yarn for a 28-G raschel lace ground yarn to have a runner length of 21.0 cm and also as a front yarn for the ground yarn to have a runner length of 100.0 cm, and then knitted together with pattern yarns of 235 dtex to 330 dtex. The resultant fabric was subjected to scouring, dyeing, and finish setting, thereby obtaining a knitted lace for innerwear use. The lace product obtained was evaluated, and the results thereof are shown in Table 1

Example 2

A nylon-6 multifilament having a fineness of 33 dtex and including 5 filaments and a knitted lace were obtained in the same manner as in Example 1, except that the strength and the knot strength were changed by setting the relaxing ratio between the second drawing roller 9 and the relaxing roller 10 to 0%. The evaluation results are shown in Table 1.

Example 3

A nylon-6 multifilament having a fineness of 33 dtex and including 5 filaments and a knitted lace were obtained in the same manner as in Example 1, except that the strength and the knot strength were changed by setting the relaxing ratio between the second drawing roller 9 and the relaxing roller 10 to 1.5%. The evaluation results are shown in Table 1.

Example 4

A nylon-66 multifilament having a fineness of 33 dtex and including 5 filaments and a knitted lace were obtained in the same manner as in Example 1, except that nylon-66 (N66) chips having a sulfuric acid relative viscosity (ηr) of 3.2 and a melting point of 265° C. were used as a polyamide. The evaluation results are shown in Table 1.

Comparative Example 1

A nylon-6 multifilament having a fineness of 33 dtex and including 5 filaments and a knitted lace were obtained in the same manner as in Example 1, except that the relaxing ratio between the second drawing roller 9 and the relaxing roller 10 was 2.0% and the knot strength was 5.9 cN/dtex. The evaluation results are shown in Table 1.

Since the relaxing ratio was 2.0%, heat setting was performed in a state where the relaxation was large, the linearity of the molecular chain was lowered, and the knot strength was lowered. Therefore, the durability of the knitted lace was poor.

TABLE 1 Example Example Example Example Comparative 1 2 3 4 Example 1 Polymer Polyamide N6 N6 N6 N66 N6 Spinning Fluid swirling Yes Yes Yes Yes Yes condition nozzle device Injection pressure 0.1 0.1 0.1 0.1 0.1 of swirling flow (MPa) Stage number of 2 2 2 2 2 drawing Relaxing ratio (%) 1.0 0 1.5 1.0 2.0 Yarn Total fineness 33 33 33 33 33 property (dtex) Filament number 5 5 5 5 5 Single-filament 6.6 6.6 6.6 6.6 6.6 fineness (dtex) Elongation (%) 27.0 23.0 33.0 27.0 34.0 Strength (cN/dtex) 7.7 8.3 7.5 7.8 7.5 Strength-elongation 9.8 10.2 10.0 9.9 10.1 product (cN/dtex) Knot strength 6.7 7.3 6.2 6.6 5.9 (cN/dtex) 15% strength 6.5 7.0 6.1 6.6 6.2 (cN/dtex) U % 0.7 0.6 0.6 0.7 0.7 Fluff number 0.3 0.5 0.2 0.3 0.2 (/100,000) Evaluation Softness S S S S S of lace Durability S S A S C Product appearance S S A S S quality (fluff) Process passage S S S S S capability

Example 5

A nylon-6 multifilament having a fineness of 22 dtex and including 7 filaments and a knitted lace were obtained in the same manner as in Example 1, except that the spinneret used had an ejection amount of 38.6 g/min and 42 holes, and was for producing 6 yarns per spinneret. The evaluation results are shown in Table 2. The durability of the knitted lace was good, the durability was maintained while the fineness was enhanced, and the texture was soft. Further, as the fineness was enhanced, the transparency of the ground lace yarn was increased, and the pattern looked more beautiful than in Example 1.

Example 6

A nylon-6 multifilament having a fineness of 22 dtex and including 20 filaments and a knitted lace were obtained in the same manner as in Example 1, except that the spinneret used had an ejection amount of 25.8 g/min, 80 holes, and a diameter of 0.18, and was for producing 4 yarns per spinneret. The evaluation results are shown in Table 2. The durability of the knitted lace was good, the durability was maintained even when the fineness was enhanced, and the texture was very soft. Further, as the fineness was enhanced, the transparency of the ground lace yarn was increased, and the pattern looked more beautiful than in Example 1.

Example 7

A nylon-6 multifilament having a fineness of 42 dtex and including 6 filaments and a knitted lace were obtained in the same manner as in Example 1, except that the spinneret used had an ejection amount of 49.2 g/min, 24 holes, and a diameter of 0.30, and was for producing 4 yarns per spinneret. The evaluation results are shown in Table 2. The knitted lace had good durability and a soft texture. Further, since the U % was very good, it was a knitted lace with no uneven dyeing as compared with Example 1.

Comparative Example 2

A nylon-6 multifilament having a fineness of 33 dtex and including 5 filaments and a knitted lace were obtained in the same manner as in Example 1, except that the fluid swirling nozzle device 6 was not installed. The evaluation results are shown in Table 2.

Since the single-filament fineness was high in a high fineness or high single-filament fineness region for clothing, when the entanglement treatment was performed during the drawing, the entanglement of the single yarn occurred, the drawability of the yarn at the entanglement point decreased, the strength decreased, and fluffing frequently occurred. Therefore, the knitted lace was poor in process passage capability, durability, and product appearance quality (fluffing).

Comparative Example 3

A nylon-6 multifilament having a fineness of 150 dtex and including 5 filaments and a knitted lace were obtained in the same manner as in Example 1, except that the fluid swirling nozzle device 6 was not installed and the spinneret used had an ejection amount of 43.9 g/min, 5 holes, and a diameter of 0.50, and was for producing 1 yarn per spinneret. The evaluation results are shown in Table 2.

Since the fineness and the single-filament fineness were high, the knitted lace was poor in softness. Further, since the fineness of the ground yarn was large, the ground lace yarn had no transparency and the pattern did not look beautiful.

Comparative Example 4

A nylon-6 multifilament having a fineness of 22 dtex and including 32 filaments and a knitted lace were obtained in the same manner as in Example 1, except that the spinneret used had an ejection amount of 19.3 g/min, 96 holes, and a diameter of 0.16, and was for producing 3 yarns per spinneret. The evaluation results are shown in Table 2.

Since the single-filament fineness was smaller than in Examples 5 and 6, the texture was improved, but the polyamide fiber was rapidly cooled in cooling part, the drawability was lowered, the strength and the knot strength were lowered, the U % was deteriorated, and the fluffing was also increased. Therefore, the knitted lace was poor in process passage capability, durability, and product appearance quality (fluffing, unevenness).

Comparative Example 5

A nylon-6 multifilament having a fineness of 33 dtex and including 5 filaments and a knitted lace were obtained in the same manner as in Example 1, except that, as shown in the FIG. 2, the second drawing roller 9 and the relaxing roller 10 were not installed, only one stage of drawing was performed in the take-up roller 7 and the first drawing roller 8 such that the draw ratio between the take-up roller 7 and the first drawing roller 8 was 4.35 times, and relaxation was performed at a relaxing ratio of 1.0% between the first drawing roller 8 and the winding device 12. The evaluation results are shown in Table 2.

Since high-ratio drawing was performed in the one stage drawing, the drawability deteriorated, the strength was lowered, and fluffing occurred. Therefore, the knitted lace was poor in process passage capability, product appearance quality (fluffing), and durability.

Comparative Example 6

A nylon-6 multifilament having a fineness of 33 dtex and including 5 filaments and a knitted lace were obtained in the same manner as in Example 1, except that, as shown in the FIG. 2, the second drawing roller 9 and the relaxing roller 10 were not installed, only one stage of drawing was performed in the take-up roller 7 and the first drawing roller 8 such that the draw ratio between the take-up roller 7 and the first drawing roller 8 was 4.35 times, and relaxation was performed at a relaxing ratio of 5.0% between the first drawing roller 8 and the winding device 12. The evaluation results are shown in Table 2.

Since high-ratio drawing was performed in the one stage drawing, the drawability deteriorated, the strength was lowered, and fluffing occurred. Further, since the relaxing ratio was 5.0%, heat setting was performed in a state where the relaxation was large, the linearity of the molecular chain was lowered, and the knot strength was lowered. Therefore, the knitted lace was poor in process passage capability, appearance quality, and durability.

TABLE 2 Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 5 Ex. 6 Ex. 7 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Polymer Polyamide N6 N6 N6 N6 N6 N6 N6 N6 N6 Spinning Fluid swirling Yes Yes Yes Yes No No Yes Yes Yes condition nozzle device Injection pressure of 0.1 0.1 0.1 0.1 — — 0.1 0.1 0.1 swirling flow (MPa) Stage number of 2 2 2 2 2 2 2 1 1 drawing Relaxing ratio (%) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 5.0 Yarn Total fineness (dtex) 33 22 22 42 33 150 22 33 33 property Filament number 5 7 20 6 5 5 32 5 5 Single-filament 6.6 3.1 1.1 7.0 6.6 30.0 0.7 6.6 6.6 fineness (dtex) Elongation (%) 27.0 28.0 26.5 29.0 26.5 28.0 24.0 26.0 35.0 Strength (cN/dtex) 7.7 7.6 7.5 7.8 7.4 7.6 7.0 7.3 6.9 Strength-elongation 9.8 9.7 9.5 10.1 9.4 9.7 8.7 9.2 9.3 product (cN/dtex) Knot strength (cN/dtex) 6.7 6.6 6.1 6.6 6.6 6.7 5.4 6.4 5.7 15% strength (cN/dtex) 6.5 6.5 6.0 6.6 6.3 6.6 4.9 6.4 6.1 U % 0.7 0.8 1.2 0.5 0.6 0.4 1.8 0.7 0.6 Fluff number 0.3 0.4 0.4 0.2 13.1 0.3 0.6 8.9 8.5 (/100,000 m) Evaluation Softness S S S A S C S S S of lace Durability S A A S C S C B C Product appearance S S S S C S B C C quality (fluffing) Process passage S S S S C S S C C capability

Although our multifilaments and knitted lace has been described in detail using specific examples, it is apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of this disclosure. This application is based on Japanese Patent Application No. 2018-10324 filed on Jan. 25, 2018, the entire contents of which are incorporated herein by reference. 

1-6. (canceled)
 7. A polyamide multifilament having a single-filament fineness of 0.8 dtex to 7 dtex, a strength of 7.5 cN/dtex to 8.5 cN/dtex, and a knot strength of 6.0 cN/dtex to 7.5 cN/dtex.
 8. The polyamide multifilament according to claim 7, having a tensile strength at 15% elongation of 6.1 cN/dtex to 7.5 cN/dtex.
 9. The polyamide multifilament according to claim 7, having a total fineness of 20 dtex to 44 dtex.
 10. A knitted lace produced using the polyamide multifilament according to claim 7 as a ground lace yarn.
 11. A method of producing the polyamide multifilament according to claim 7, the method comprising: ejecting a molten polyamide resin from a spinneret to form filaments; cooling and solidifying each of the filaments; and drawing the obtained filaments, wherein the method is performed using a polyamide multifilament production device including at least: a spinneret that ejects a molten polyamide resin to form filaments; a heating cylinder to gradually cool the filaments; a cooling device that cools and solidifies the filaments; a fluid swirling nozzle device for imparting convergence to yarns by a swirling flow; a take-up roller for taking-up and drawing the filaments; and a drawing device for drawing the filaments, and wherein conditions (A) to (D) are satisfied: (A) the heating cylinder is provided above the cooling device; (B) the fluid swirling nozzle device is provided above the take-up roller; (C) the drawing device is a multi-stage drawing device having two or more stages; and (D) a low relaxation heat treatment is performed immediately after multi-stage drawing.
 12. The method according to claim 11, wherein the relaxation heat treatment is performed between a drawing roller and a relaxing roller at a relaxing ratio of 0 to 1.5% and a heat set temperature of 150° C. to 200° C.
 13. The polyamide multifilament according to claim 8, having a total fineness of 20 dtex to 44 dtex.
 14. A knitted lace produced using the polyamide multifilament according to claim 8 as a ground lace yarn.
 15. A knitted lace produced using the polyamide multifilament according to claim 9 as a ground lace yarn.
 16. A knitted lace produced using the polyamide multifilament according to claim 13 as a ground lace yarn.
 17. A method of producing the polyamide multifilament according to claim 8, the method comprising: ejecting a molten polyamide resin from a spinneret to form filaments; cooling and solidifying each of the filaments; and drawing the obtained filaments, wherein the method is performed using a polyamide multifilament production device including at least: a spinneret that ejects a molten polyamide resin to form filaments; a heating cylinder that gradually cools the filaments; a cooling device that cools and solidifies the filaments; a fluid swirling nozzle device that imparts convergence to yarns by a swirling flow; a take-up roller that takes-up and draws the filaments; and a drawing device that draws the filaments, and wherein conditions (A) to (D) are satisfied: (A) the heating cylinder is provided above the cooling device; (B) the fluid swirling nozzle device is provided above the take-up roller; (C) the drawing device is a multi-stage drawing device having two or more stages; and (D) a low relaxation heat treatment is performed immediately after multi-stage drawing.
 18. A method of producing the polyamide multifilament according to claim 9, the method comprising: ejecting a molten polyamide resin from a spinneret to form filaments; cooling and solidifying each of the filaments; and drawing the obtained filaments, wherein the method is performed using a polyamide multifilament production device including at least: a spinneret that ejects a molten polyamide resin to form filaments; a heating cylinder to gradually cool the filaments; a cooling device that cools and solidifies the filaments; a fluid swirling nozzle device that imparts convergence to yarns by a swirling flow; a take-up roller that takes-up and draws the filaments; and a drawing device that draws the filaments, and wherein conditions (A) to (D) are satisfied: (A) the heating cylinder is provided above the cooling device; (B) the fluid swirling nozzle device is provided above the take-up roller; (C) the drawing device is a multi-stage drawing device having two or more stages; and (D) a low relaxation heat treatment is performed immediately after multi-stage drawing.
 19. A method of producing the polyamide multifilament according to claim 13, the method comprising: ejecting a molten polyamide resin from a spinneret to form filaments; cooling and solidifying each of the filaments; and drawing the obtained filaments, wherein the method is performed using a polyamide multifilament production device including at least: a spinneret that ejects a molten polyamide resin to form filaments; a heating cylinder that gradually cools the filaments; a cooling device that cools and solidifies the filaments; a fluid swirling nozzle device that imparts convergence to yarns by a swirling flow; a take-up roller that takes-up and draws the filaments; and a drawing device that draws the filaments, and wherein conditions (A) to (D) are satisfied: (A) the heating cylinder is provided above the cooling device; (B) the fluid swirling nozzle device is provided above the take-up roller; (C) the drawing device is a multi-stage drawing device having two or more stages; and (D) a low relaxation heat treatment is performed immediately after multi-stage drawing.
 20. The method according to claim 17, wherein the relaxation heat treatment is performed between a drawing roller and a relaxing roller at a relaxing ratio of 0 to 1.5% and a heat set temperature of 150° C. to 200° C.
 21. The method according to claim 18, wherein the relaxation heat treatment is performed between a drawing roller and a relaxing roller at a relaxing ratio of 0 to 1.5% and a heat set temperature of 150° C. to 200° C.
 22. The method according to claim 19, wherein the relaxation heat treatment is performed between a drawing roller and a relaxing roller at a relaxing ratio of 0 to 1.5% and a heat set temperature of 150° C. to 200° C. 